1. Field of the Invention
The subject invention relates to a prosthetic temporomandibular joint.
2. Description of the Related Art
The prior art temporomandibular joint prosthesis includes a condyle component attached to the lower jaw and a fossa component attached to the upper jaw. The condyle components have included a mounting portion in the form of a generally planar support having apertures therethrough for receiving screws. The support is positioned adjacent the ramus and is secured in that position by screws passing through the apertures in the support. A neck extends from the support, and a condyle extends from the neck. The condyle of some prior art temporomandibular joint prostheses is spherical. On other prior art prostheses, the condyle is substantially an ellipsoid that is elongated in a general medial to lateral direction. The fossa component of the prior art temporomandibular joint typically has been in the form of a thin bearing having a superior surface that is mounted to the fossa and an inferior surface that is configured to be congruent with the condyle and that engages the condyle in articular bearing engagement. Examples of such prior art prosthetic temporomandibular joints are shown in U.S. Pat. No. 4,778,472; U.S. Pat. No. 4,936,852 and U.S. Pat. No. 5,445,650.
The prior art temporomandibular joint prosthesis having a high degree of congruency between the condyle and the fossa would be effective if the temporomandibular joint of a jaw were subject to pure pivotal movement about a medial-lateral axis. However, the temporomandibular joint is subject to a very complex and varying array of applied forces during chewing and during other normal facial movements. In particular, moments may be applied to the temporomandibular joint about an anterior-posterior axis and about a superior-inferior axis. Furthermore, anterior-posterior loads and medial-lateral loads may be applied to the condyle relative to the fossa component. In view of the complexity of these forces and moments, and in view of the relatively high loads, prior art temporomandibular joint prostheses have been subject to dislocation. Furthermore, certain loads applied to the prior art temporomandibular prosthesis may cause sufficient movement of the components to replace the intended congruent contact with a substantially point contact. The single point of contact between prosthetic components necessarily concentrates the applied load to the point of contact, and has led to component failure. Failure is particularly likely to occur in the articular bearing surface of the fossa component.
In view of the above, it is an object of the subject invention to provide a temporomandibular joint prosthesis that is better able to withstand the complex loads applied to the prosthesis.